Usable Hole Diameter

Ledges reduce usable hole diameter as is shown in the figure. One solution is to run larger collars above the drill bit. It may be reconciled from the sketch that the usable hole diameter is the sum of one-half the bit and one-half the drill collar diameters.

Thus, a collar diameter yields a specific usable hole diameter. The equation for selection a collar diameter is then

Required Collar Diameter = 2 * Usable Hole Diameter - Drill Bit Diameter

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  • alfrida
    How to drill a usable hole?
    7 years ago

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